1. Field of the Invention
The present invention relates to an air passage changeover device.
2. Description of the Related Art
Conventionally, a plate damper device that controls an air volume or changes an air flow by the rotation of a damper plate, has been put into practical use for an air passage changeover device. Japanese Unexamined Patent Publication (Kokai) No. 141116-1989 discloses a film damper that is operated in the following manner: a flexible screen, for example, made of a polyethylene film, is slid along each outlet in an air conditioner case; and the air volume blown out from the outlet is individually controlled by the amount of overlap of the outlet and a draft hole formed in a predetermined position on the polyethylene film.
However, according to the results of various investigations, the following has been found: the screen of a resin film adopted to the aforementioned conventional film damper device satisfies the requirements of tensile strength, air flow sealing property and flexibility, however, it is not practically sufficient from the viewpoint of tear strength.
That is, in order to prevent air leakage, the screen used for the air passage changeover device must be slid along the inner wall surface of the case over all the circumference of each outlet. Also, the screen is curved along drive and guide rollers, the diameter of which is relatively small. Therefore, stress is locally concentrated on the screen, so that a screen made of a resin film is torn. Accordingly, the screen cannot be put into practical use because its tear strength is insufficient.
In order to solve the problems, the inventors investigated various materials for the screen.
First, the inventors investigated rubber and fiber reinforced rubber because these can stand bending stress applied by the drive and guide rollers and, further, they are flexible. However, they are susceptible to deformation. Also, when the position and profile of the draft hole are varied, it is difficult to accurately carry out damper functions such as control of an air volume and changeover of an air flow direction. Moreover, their moisture and heat resistant properties are not good.
Although a metallic sheet has a large number of advantages, its flexibility is not good. In particular, it is difficult to curve the metallic sheet along a guide roller of a small diameter and to wind it around a drive roller of a small diameter, and the metallic sheet is susceptible to plastic deformation.
Flexibility and tear strength of fabrics are sufficiently high. However, in the case of fabrics of usual thickness, the air flow sealing property is not sufficient, and the surface of fabrics becomes rough when they are slid. Further, noises are caused by the uneven surface of fabrics, and the screen of fabrics cannot be smoothly driven since the frictional coefficient is higher than that of a resin film. Furthermore, a permanent elongation referred to as an initial elongation of fabrics is about 2. Therefore, the position of a draft hole is changed by the elongation. Accordingly, it is difficult to carry out accurate air flow control.